Hope — a faculty decidedly different from and far more muscular than optimism — remains our most potent antidote to the passivity and resignation of cynicism. The great humanistic philosopher and psychologist Erich Fromm admonished against the common laziness of optimism and pessimism, but he extolled the counterpoint to both — active hope that empowers us “to think the unthinkable, yet to act within the limits of the realistically possible.”

“Hope is a gift you don’t have to surrender, a power you don’t have to throw away,” Rebecca Solnit wrote two generations later in her lucid and luminous manifesto for our grounds for hope and action in dark times. The philosopher Jonathan Lear termed those grounds “radical hope” — the kind of hope that “anticipates a good for which those who have the hope as yet lack the appropriate concepts with which to understand it.” But such anticipation of the unimaginable is inherently in constant dialogue with the unknown — with the fearsome possibility of not obtaining the object of hope and with the concomitant potential for despair.

That necessary complementarity of hope and fear in the face of the unknown is what the great French philosopher, scientist, and mathematician René Descartes (March 31, 1596–February 11, 1650), patron saint of reason, explores in a section of The Passions of the Soul (public library) — his final published work, which gave us Descartes on the cure for indecision and how we acquire nobility of soul.

Descartes writes:

The mere fact of thinking that a good may be acquired or an evil avoided is sufficient to produce the desire for this to come to pass. But when, over and above this, we consider whether our desire is likely to be satisfied or not, the idea that it is likely arouses hope in us, and the idea that it is unlikely arouses fear, of which one variety is jealousy.

He considers the common root and complementarity of hope and fear:

Hope is a disposition of the soul to persuade itself that what it desires will come to pass, which is caused by a particular movement of the spirits, namely, by that of mingled joy and desire. And fear is another disposition of the soul, which persuades it that the thing will not come to pass. And it is to be noted that, although these two passions are contrary, one may nonetheless have them both together, that is, when one considers different reasons at the same time, some of which cause one to judge that the fulfillment of one’s desires is a straightforward matter, while others make it seem difficult.

And neither of these passions ever accompanies desire without leaving some room for the other.

Descartes argues that a severe imbalance of the two is equally deleterious, whichever direction it may tip in — just as an excess of fear may drive out all hope and leave us paralyzed to act, an excess of optimism that drives out all uncertainty and fear is just as paralytic to fruitful action, for it renders us complacent. In a sentiment that calls to mind Kierkegaard’s insistence that anxiety powers rather than hinders creativity, Descartes writes:

When hope is so strong that it altogether drives out fear, its nature changes and it becomes complacency or confidence. And when we are certain that what we desire will come to pass, even though we go on wanting it to come to pass, we nonetheless cease to be agitated by the passion of desire which caused us to look forward to the outcome with anxiety. Likewise, when fear is so extreme that it leaves no room at all for hope, it is transformed into despair; and this despair, representing the thing as impossible, extinguishes desire altogether, for desire bears only on possible things.

Half a millennium later, The Passions of the Soul remains a masterwork of extraordinary insight into the workings of the human mind, heart, and spirit. Complement this particular portion with Victoria Safford on what it means to stand at the gates of hope and E.B. White’s remarkable letter to a man who had lost hope for humanity, then revisit Descartes’s twelve timeless tenets of critical thinking.